Fire may be detected by detecting a temperature higher than a room temperature and detecting smoke. As well known in the art, a temperature detector may be designed according to a differential manner in which a variation in a temperature is sensed or according to a fixed temperature manner in which a specific temperature is sensed. A smoke detector may be designed according to an ionization manner in which ionized smoke is sensed or according to an optical manner in which light scattered due to collision of light, particles, and smoke is sensed.
FIG. 1A is a conceptual diagram schematically illustrating an ionization type smoke detector. FIG. 1B is a graph illustrating a voltage variation of an output of a smoke detector in FIG. 1A.
Referring to FIGS. 1A and 1B, a conventional ionization type smoke detector 100 may include an external ionization room 2 exposed to smoke particles 1 and an internal ionization room 3 providing a space independent from the exterior. Each of the external ionization room 2 and the internal ionization room may include a radiation source 4. The radiation sources 4 may include radiation materials (e.g., americium-241 (Am-241), radium (Ra), etc.) emitting radiation for ionizing the smoke particles 1. A switch 5 may control voltages to be applied to the external and internal ionization rooms 2 and 3 in various manners. When the smoke particles 1 don't exit at the external ionization room 2, an internal voltage Vin and an external voltage Vout may become symmetric to be identical to each other. On the other hand, a difference ΔV of external voltages Vout may be generated when the smoke particles 1 do exit at the external ionization room 2. At this time, the external voltage Vout may be lower than the internal voltage Vin. However, the conventional ionization-type smoke detector 100 may necessitate a smoke ionizing process using a harmful radiation material. That is, the conventional ionization-type smoke detector 100 may have problems of the safety.
FIG. 2 is a conceptual diagram schematically illustrating a conventional optical-type smoke detector.
Referring to FIG. 2, an optical-type smoke detector 200 may include an optical sensor 9 which is configured to sense scattered light 8. Herein, the scattered light 8 may be generated when light output from a light source 6 is scattered by smoke particles 1. The optical sensor 9 may be installed at a closed place to have a space independent from the outside. The independent space for installation of the optical sensor 9 may cause an increase in an installation cost. Also, the conventional optical-type smoke detector 200 may necessitate a high-performance optical sensor 9 for sensing the scattered light 8. That is, the productivity of the optical-type smoke detector 200 may be low.